87
votes
How many times do you have to circle the Earth to break orbit?
This depends on how much thrust you have available. With enough thrust, you don't need to be in Earth orbit at all: you can launch straight into an escape trajectory.
New Horizons did this, more or ...
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78
votes
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Shouldn't space junk fall back to Earth on its own? How long will take for a ~1 cm piece of junk in LEO to fall back to Earth on its own for example?
It depends on the altitude. Here is a chart from ESA and UNOOSA. Basically, anything under 500 km will fall relatively quickly, maybe 25 years. Everything under 800 km should fall within a century or ...
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70
votes
Where does space begin on planets without atmospheres?
Yet surely nobody would classify Neil Armstrong's lunar bunny-hops as suborbital spaceflights.
Why not? There's no essential difference between a high-eccentricity trajectory with an apolune of 1 ...
- 160k
66
votes
Accepted
What is the farthest artificial satellite in orbit in our solar system?
The term for orbits in our solar system around the Sun is Heliocentric.
Closed Heliocentric Orbit
The solar observation probe Ulysses is the furthest artificial satellite around the sun. It's in a ...
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66
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Why can't you travel to Mars in a straight line?
Only answering your first question here, and in qualitative terms:
You can't travel to Mars in a straight line for the same reasons you can't throw a ball in a straight line: gravity. If you wanted to ...
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64
votes
Why aren't the 'bedrooms' aboard the ISS also the escape pods?
Primarily, because without a lot of extra equipment, they could at best be space coffins for the astronauts.
First, they share life support with the rest of the station. Air circulated through them ...
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61
votes
Why doesn't ISS pass over the polar regions?
The decision to orbit (and assemble) the International Space Station (ISS) in 51.65° prograde Low Earth Orbit (LEO) was driven by its accessibility and utility. You see, inclination changes are ...
- 75.5k
60
votes
Why are all space initiatives designed to get to space overnight when in Nature all extreme feats are achieved in a gradual process
Imagine you have a very heavy book and a bookcase, and your goal is to put the book on the top shelf of the bookcase. How much time would you spend doing that? Maybe five seconds, maybe fifteen. Would ...
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59
votes
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Why do artificial satellites need orbit correction, but natural ones don't?
The instability in orbits of our artificial satellites come from a few basic causes:
Atmospheric drag and solar wind effects
The Earth isn't a perfect uniform sphere but is slightly lumpy, which ...
- 160k
55
votes
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What does the Sun-Earth-Moon system look like from the Sun-Earth L-2 point?
I treated this as a problem of geometry and came up with this:
The sun is the large yellow disk.
The earth is the largest black disk, obscuring most of the sun
The left-hand dark-grey disk is the ...
- 2,710
51
votes
Why are all trajectories in space a conic sections?
Not all trajectories in space are conic sections, only those that are a two body problem. One planet in orbit around a star is a two body problem. Only two body problems are solved by a conic section.
...
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49
votes
Accepted
Determining orbital position at a future point in time
Statement of the Problem
The problem you want to solve is called the Kepler problem. In your formulation of the problem, you're starting out with the Cartesian orbital state vectors (also called ...
- 2,490
46
votes
How many times do you have to circle the Earth to break orbit?
Zero
See at: https://en.wikipedia.org/wiki/Escape_velocity for theory.
Once you build enough velocity to surpass gravitational attraction, you will leave planetary orbit. A spacecraft simply ...
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46
votes
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Do you need 0 km/s velocity to crash into the sun?
Wouldn't i inevitably spiral to sun surface even if i was faster than 0km/s ?
No. On reasonable timescales, an orbit will have a fixed distance of closest approach, called "periapsis." (These ...
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45
votes
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Are all satellites of all planets in the same plane?
Most large regular satellites orbit in the equatorial plane of their planet. Every planet spins, and thus has an equatorial bulge caused by centrifugal forces that over time aligns the satellites' ...
- 496
44
votes
Escaping moons conflict with what I understand of gravity
A very good question!
The reason is essentially to do with tides. And a slightly over-simplified summary is: If the moon orbits more slowly than the rotation of the parent body (as our Moon does, 12 ...
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42
votes
Why do artificial satellites need orbit correction, but natural ones don't?
Essentially, this is a result of observational bias. A natural satellite will only orbit a parent for extended time periods precisely because the orbit it is in is stable †.
The plain truth of the ...
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41
votes
Accepted
Why use a retrograde orbit?
Retrograde orbits have multiple use-cases. First of all you should note that "retrograde" doesn't mean 180° inclination - everything > 90° is considered retrograde. This places all sun-synchronous ...
- 6,770
41
votes
If the Earth spun clockwise, how would that affect Space Exploration?
Primarily, locations of spaceports would change. California, not Florida would host the NASA's main launch site. Russia would be in slightly better position, able to send rockets over the Black Sea, ...
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37
votes
Accepted
Requirements to orbit Pluto
This mission study came up with a 900 kg nuclear-electric-propulsion spacecraft launched on an Ariane V with a C3 of 100 km2/s2 and a Jupiter gravity assist along the way. 1.05 kW electrical power at ...
- 57.6k
37
votes
Do simulator games use a realistic trajectory to get into orbit?
I understand the reasons behind each of this manouveurs, however I'm wondering if this is how real rockets get into orbit.
Cutting off the engine and letting the rocket loose vertical speed looks ...
- 160k
36
votes
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How does a Spacecraft change its orbit?
To answer your title question: By using its engines.
However you seems to be quite puzzled by the fact that velocity of an object can decrease and increase over the course of an orbit.
If the orbit ...
- 12.2k
35
votes
Where does space begin on planets without atmospheres?
Ultimately, "the edge of space" is an agreed upon convention. In other words it is essentially arbitrary, something which only humans even care about (well maybe space aliens too <grin>). Yes, ...
- 459
34
votes
Do simulator games use a realistic trajectory to get into orbit?
Physics
In regards to the physics, KSP is fairly realistic, other than it not modeling n-body physics (which isn't really relevant in scope of orbiting Earth/Kerbin).
In regards to the engineering, ...
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33
votes
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How did the USSR track Gagarin's Vostok-1 orbital flight? Was tracking capability an issue in the choice of orbit?
The Answer is on a page by Sven Grahn.
No ocean going tracking ships were used. Only ground stations on the territory of the USSR.
In the other answers some russian sources about the use of tracking ...
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32
votes
Why did the X-15 not achieve orbit?
You're confusing units. The maximum speed of the X-15 was 7274 km/h, or about 2 km/s. Orbital speed is around 8 km/s. The X-15 didn't carry enough fuel to reach orbital speed.
- 121k
32
votes
Accepted
How is the altitude of a satellite defined, given that the Earth is not spherical?
update: 6378.137 km is what I use now.
By convention the altitude of a spacecraft is the distance to the center of the Earth minus roughly 6378 kilometers, or some reference radius that is ...
- 148k
31
votes
Accepted
Is this really Rosetta's orbit around 67P?
This was one of the questions just now during the Rosetta press briefing. This video was shown during the presentation:
The triangular trajectory are hyperbolic ...
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30
votes
Accepted
Why are the GPS constellation satellites in such a high orbit?
The main reason they are in such a high orbit is to allow for more of the Earth to be visible at any one time. In order to have a reasonable amount of the Earth visible, you have to be high up. A ...
- 118k
30
votes
Accepted
This orbit looks wrong near a Lagrange point. Is it?
Is the orbit shown in the graphic wrong, or is my understanding of orbital mechanics lacking, having only been influenced by KSP?
It's not an either-or question.
The graphic is "wrong" from the ...
- 64.6k
Only top scored, non community-wiki answers of a minimum length are eligible